Monday, July 30, 2007

Scientists map elephant evolution

Scientists say they have calculated the date at which the African and the Asian elephant went their separate ways.

The two elephant species diverged from a common ancestor some 7.6 million years ago, experts working in the US, Germany and Switzerland say.

They came to their conclusion after comparing a genetic analysis of the two species with material derived from the extinct woolly mammoth and mastodon.

The African elephant is much bigger than its Asian counterpart.

It is known for its large, floppy ears, and both sexes have great ivory tusks - unlike the Asian species, in which typically only the males have large external tusks.

The now extinct mastodon was very similar in appearance to the woolly mammoth - with lots of hair and big tusks.

Genetically, however, it was very different and is only a distant relative of the elephants.

Its genetic profile had not previously been mapped, but now thanks to the analysis of material extracted from a fossilised tooth found on the banks of an Alaskan river, scientists have the first genetic portrait of the creature.

By comparing the mastodon's genetic make-up with existing genome sequences for modern elephants and the woolly mammoth, they have built up a family tree for the elephants.

The tree has the African elephant diverging from both the Asian elephant and the mammoth about 7.6 million years ago.

Then, at 6.7 million years ago, the Asian elephant and the mammoth also go their separate ways.

"The cool thing about the mastodon is that we know pretty exactly from the fossil record when it diverged from the elephant and the mammoth," said Dr Michael Hofreiter of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and one of the lead researchers.

"So using that time point and the genetic data, we could date when the African elephant, Asian elephant and mammoth diverged from each other," Dr Hofreiter explained.

"That took place in Africa in the same place where humans, chimps and gorillas diverged."

The fact that it is now judged that the elephants went their separate ways in the same place and at about the same time we humans diverged from our ape brethren may of course be a coincidence.

Or, as Dr Hofreiter suggests, there may be a common environmental or climatic event which set both elephants and humans on their eventual evolutionary course.